Sidokar, I don't live on the internet, it's been 8 hours. Please give people time to respond. As for the quality of he music, it's not meant to be high qaulity, it's my second time composing in my software for learning. Qazsedcft, I did mean Major 2nd intervals. So, that clears that up. I think you guys are getting confused because the music example was not the Cantus Firmus, or anything to do with it. I should have clarified better. The image is to a stand alone measure for learning passing notes. Hence, wondering if 'A' was a passing note in the way it lied between G chord and C chord. Or does the G note get in the way of that.
Thanks for replying all that info Sidokar, I'll try to soak it in, but it seems a little advanced for what I'm messing with right now, which is just passing notes.
"The A is not really a passing tone, since it forms a perfectly valid harmony with the C."
The videos always say a passing note is any tone outside the chord.
There are sometimes people who post questions, there are many answers and the OP never comes back. That can be frustrating at times, but obviously not the case here. Of course 8 hours or 24 hours is perfectly fine.
The seconds are valid, but not necessarily major second. It has to be diatonic second, ie in the scale. In strict counterpoint, intervals for the chant that are forbidden are all chromatic, augmented, diminished, major sixth, seventh and ninth. There are rules for octaves, like never do an octave on a leading tone. There are other rules, for example for sequences of 3 notes, like you should avoid the triton in an isolated group of 3 notes, and there are accepted workarounds that minimize the effect. If you have a teacher, and a good course, he will give you all that you need to know in a gradual way.
There is no issue with trying to compose, one is necessarily clumsy the first times. You just need someone to tell you what is correct and what should be avoided. If you are composing in counterpoint, you should start first with 2 voices, note against note or 2 notes against the chant. If you are composing homophonic, you need to know how to sequence chords and manage the bass.
Your statement about the passing tone definition in the vid is correct. But that is not what you composed. The passing tone implies that you maintain the previous harmony while playing against it the passing tone. In your example, you stopped the G chord and introduced a new harmony with the C in the bass, a 6th chord CA. A would have been a passing tone had you maintained the G harmony while playing A. In general passing tones are often used on weak beats. Now you can see A as an appogiatura of the subsequent G note, since the C triad seems to be your final harmony. The best way to compose is to start with 2 voices, the melody and put the the bass line against it, and then work out the harmonies and various ornamental, passing notes.